This invention relates to a coreless motor which effectively utilizes almost the entire area of the rotor winding for the generation of torque, and the manufacturing method for the coreless motor.
Various coreless motors using air-core rotor windings are already known, but in these coreless motors only some of the area of the rotor winding effectively generates torque, and it is difficult in principle to obtain a high efficiency. Among these coreless motors, the so-called cup-shape coreless motor in which the rotor winding is formed in a cylindrical shape by winding the insulation coated conductor inreverse at the upper and lower edges and winding it obliquely makes it possible to obtain a relatively high efficiency. This type of coreless motor is described in U.S. Pat. No. 3,191,081. In the structure of this coreless motor, however, almost the entire area of the rotor winding crosses the magnetic flux at a right angle; an ineffective portion where the current flowing to the conductor flows in the reverse direction is formed, and the effective portion where the current flow in the same direction will be less than half of the entire area. Moreover, as the conductor is wound obliquely, the effective portion in the vertical direction which generates torque will be further reduced.
Another example is a coreless motor shown in U.S. Pat. No. 2,513,410. The coreless motor is of such structure that a rotor frame consisting of insulated material is designed to be rotated freely so as to enclose a cylindrical permanent magnet at predetermined gaps on the outside of this magnet; the air-core cylindrical rotor winding around which the insulation-coated conductor is entirely wound is formed on this rotor frame; yokes are arranged at gaps on the circumference face of magnet; the circumference face of said rotor winding is arranged to be rotated freely in the magnetic field gap of ring shape between this magnet and yoke.
In this coreless motor, however, the magnetic flux does not act on the upper and lower plane portions of the rotor winding, and these portions become ineffective ones which do not generate torque.
In addition, as the magnet is located inside the rotor winding, the size of the magnet is limited, and therefore it becomes impossible to obtain sufficient motor torque.